Angiographic and guide catheters are well known in the field of medicine for use in conjunction with other catheters for the treatment of cardiovascular disease through such procedures as percutaneous transluminal coronary angioplasty (PTCA) procedures. Guide catheters aid in treatment of arterial lesions by providing a conduit for positioning dilatation balloon systems across an arterial stenosis. The need for a greater variety of guide catheters to treat different types of circumstances has grown tremendously as the techniques for the use of such devices has grown.
During the treatment of cardiovascular disease, the catheter must be able to traverse tortuous pathways through blood vessels in a manner that minimizes trauma. In order for the physician to place the catheter at the correct location in the vessel, the physician must apply longitudinal and rotational forces. The catheter must be stiff enough to resist the formation of kinks, while at the same time, the catheter must possess flexibility to be responsive to maneuvering forces when guiding the catheter through the vascular system. The catheter must be rigid enough to push through the blood vessel, but yet flexible enough to navigate the bends in the blood vessel. The guide or angiographic catheter must exhibit good torque control such that manipulation of a proximal portion of the catheter is responsively translated to the tip or distal end of the catheter to curve and guide the catheter through the tortuous pathways. Thus, the catheter must have torsional rigidity to transmit the applied torque. To accomplish this, balance between longitudinal rigidity, torsional rigidity and flexibility, often times a support member is added to the shaft. This support member is often comprised of a metal braid or a coil embedded in the shaft.
In many applications, the catheter is guided through the aorta over the aortic arch and down to the ostium of the vessel which is to be treated. It is preferable to have a soft tip or flexible section engage the ostium. Therefore, it is advantageous to have the proximal section more rigid to transmit the forces applied, but have the distal end more flexible to allow for better placement of the catheter. Having the distal section more flexible also creates a less traumatic section to contact the blood vessel. The distal end of the catheter is rotated, through the transmission of torque from the proximal end, until the tip of the catheter is in the desired position. With the variation of different bend shapes available on the distal ends of these devices and with variations in patient anatomy, each device may need to be torqued more or less in order to correctly place it.
In order to meet these performance requirements, catheters are often manufactured using polymers in conjunction with the above-mentioned support member using a metal braid or coil, wherein the support member is incorporated into the tube of the guide catheter. Catheters can be formed of three layers. An inner tubular member is used which defines an inner lumen which may be formed of a material that decreases the coefficient of friction such as that encountered between a balloon catheter and the inner lumen of the catheter. The support member conforms to the outside of the inner layer and is often comprised of a metal braid or coil. The third outer tube is commonly formed from a polymer and overlays the support member.
In order to meet the above requirements of rigidity and flexibility, a catheter is desired which has regions of varying stiffness which may be readily changed during manufacturing to meet the need for the greater variety of devices necessary to treat different types of circumstances.
An example of one approach is described in U.S. Pat. No. 5,533,985, issued Jul. 9, 1996 to James C. Wang, for Tubing, which is incorporated herein by reference. Wang discloses differential stiffness tubing for medical products, including catheters, wherein the tubing has a stiff section and a flexible section joined by a relatively short transition section in which the materials of the stiff and flexible sections are joined into each other in a smooth gradual manner to produce an inseparable bond between the materials without abrupt joints. This tubing is manufactured using an extrusion process and may be limited in its ability to manufacture catheters having the desired number of regions of varying stiffness and the ability to easily accommodate product design changes during manufacture.
Catheters may be manufactured using this approach, but its practical application may be limited to joining two materials to form two zones of flexibility with a transition therebetween. Thus, with this approach, additional manufacturing steps are necessary to provide for additional regions. These regions of varying stiffness are necessary to provide rigidity to push the catheter through the blood vessel, flexibility to navigate the bends in the blood vessel, and torsional stiffness to correctly place the catheter by maintaining torque control without excessive energy storage which can cause undesirable movement of the catheter end.
It is advantageous that the catheter be visible in a fluoroscope or other form of x-ray, so that the catheter can be positioned with precision. In the prior art, this has been accomplished by applying a metal ring to the catheter adjacent the distal end. It is generally undesirable to place the metal ring exactly on the distal tip of the catheter, since the distal tip needs to be very soft and pliable. Therefore, the metal ring does not completely resolve the problem of precisely locating the distal tip of the catheter within the body by means of a fluoroscope during a medical procedure, since the metal ring is and must. be spaced from the distal tip. In other prior art, the distal tip has been manufactured to be substantially more radiopaque than portions of the catheter proximal to the tip.